1. Field of the Invention
The present invention relates generally to a rotary particulate separator for removing particulates from a pressurized gas stream such as that emanating from a reactor vessel, and more particularly to a particulate separator which utilizes a charge placed on particles in the gas stream first to induce them from the main flow path into a vortex generator, and then to carry the charged particles with a rotor located in the vortex generator into a vortex generated by a control gas flow which draws the particles radially inwardly into an exit aperture and out from the device.
2. Description of Background Information
A wide variety of devices either utilize gas as a working fluid to remove particulates from an operating environment or produce a gaseous stream containing particulates which are released by an operating environment. In either case, a gas stream is produced by a multitude of different systems, and that gas stream must be cleaned to remove the particulates prior to discharging the gas stream into the environment. One particular example of such an operating environment which presents particular problems is that of a reactor vessel producing a high pressure gas stream containing particulates which must be removed and collected for proper disposal.
As might be expected, the art is replete with examples of devices for removing particulates from a gas stream. Most of the early particulate separators are mechanical filters having a barrier construction which allows gas to flow therethrough. Such mechanical filters are quite effective in removing particulates having a sufficiently large physical size so as to enable the mechanical filter to trap the particulates. However, in many systems in use today, including the reactor environment contemplated herein, particulates produced are too fine to become trapped in a mechanical filter unless the filter is sufficiently small, in which case the particulates tend to quickly clog the filter.
Particulates in the reactor environment contemplated herein have a typical diameter of approximately two to five microns, with the gas stream having a typical pressure of 300 to 400 PSI. The particulates must be removed from the high pressure gas stream, which emanates from the reactor vessel on a continuous basis, thereby necessitating continuous processing rather than batch processing. Given the particulate size of two to five microns, the settling rate is from 0.7 to 4.4 inches per second, as per Stoke's law.
A vast number of references exist which utilize various types of electrostatic precipitation. The simplest of these devices is the basic electrostatic precipitator which places a charge on particulates, and uses electrostatic force to collect them at a collection location in the device. Examples of such devices are found in
U.S. Pat. No. 3,400,513, to Boll, in U.S. Pat. No. 3,820,306, to Vincent, and in U.S. Pat. No. 4,544,382, to Taillet et al.
The Boll patent has a gas stream ducted into and out of a housing, with particulates in the gas stream being charged upon entering the housing and collected by a precipitator. The Vincent device is made of a plurality of charged plates with dielectric plates (or grids) therebetween, with the dielectric plates receiving induced potentials and causing precipitation of particles. The Taillet et al. patent uses ion generators to produce space charges in an enclosure in which the gas stream containing particulates flows, thus initiating precipitation of the particulates.
The next step in increasing complexity of electrostatic precipitators involves the addition of a filter element to entrap particles drawn into the filter element by electrostatic force. Devices utilizing this type of construction are illustrated in U.S. Pat. No. 4,339,782, to Yu et al., in U.S. Pat. No. 4,501,598, to Long, and in U.S. Pat. No. 4,871,515, to Reichle et al.
The Yu et al. patent illustrates an
ionizer utilized to charge particulates in a gas stream, with a charged filter element being used to electrostatically attract and contain particulates in the gas stream. The Long reference uses a filter element disposed in the gas flow, with portions of the filter medium fluttering to generate electrostatic charges to attract and remove particulates from the gas stream. The Reichle et al. patent uses a filter element containing "windshadow areas," which shield trapped particles from the gas stream to prevent them from reentering the gas stream once trapped in the filter by electrostatic separation.
An enhancement to electrostatic separation using a fixed filter is illustrated in U.S. Pat. No. 3,783,588, to Hudis, and in U.S. Pat. No. 4,229,187, to Stockford et al. In the Hudis patent, moving sheets of filter material are passed through a gas stream, with electrostatic charge being used to attract particulates to the sheets. The sheets may be cleaned when they are not contained in the gas stream. The Stockford et al. reference teaches the use of a filter media which develops an electrostatic charge in a dry, fast gas stream.
A more complex type of electrostatic precipitator is taught in U.S. Pat. No. 4,093,430, to Schwab et al., and in U.S. Pat. No. 4,846,430, to Burger et al. These devices charge particles in the gas stream and remove them in a wet process known as "scrubbing." The Schwab et al. reference uses a dense electrostatic field to charge particulates which may then be removed by a scrubber. The Burger et al. patent teaches dispersing scrubbing liquid into the gas stream and then ionizing the particulates and liquid droplets, which are removed by a high speed brush charged to attract the particulates and the droplets.
These devices discussed briefly above are all useful in their preferred environments, but are not acceptable for use with the reactor to remove the contaminated particulates in the high pressure gas stream leaving the reactor vessel. The high pressure, continuous flow characteristics of the reactor combined with the necessity for complete removal of the particulates present a situation the devices discussed above are not able to cope with in an acceptable manner.
To date, the only devices which have been even close to acceptable in particulate removal characteristics are centrifugal type devices rather than electrostatic filters. Even these devices have not been completely successful. Looking once again at the art for further variations, two additional references have been located, both of which combine centrifugal force with electrostatic attraction of particulates. These devices are illustrated in U.S. Pat. No. 4,134,744, to Peterson et al., and in U.S. Pat. No. 4,398,928, to Kunsagi.
The Peterson et al. device is designed for an industrial application, and has a disk with plural pie-shaped segments through which the gas stream is directed. Alternating segments of the disk are charged with opposite polarities, and dielectric fluid is supplied to the center of the disk. The disk is spun to flow the dielectric fluid radially outwardly, and the charges on the segments of the disk attract particulates in the gas stream. The dielectric fluid thus washes particulates attracted to the disk outwardly, where the charge is neutralized and the fluid, together with the particulates, is collected.
While the Peterson et al. device represents an interesting approach, it simply is not suitable for the high pressure reactor application contemplated herein. The particulates in the gas stream are not precharged, and since they are very small, they may well flow through the disk and not be removed. In addition, the use of the dielectric fluid creates an additional waste disposal problem, exacerbating the situation instead of improving it.
Finally, the Kunsagi reference teaches a centrifugal separator using a nozzle directed tangentially to impart a high rotational velocity to the gas stream in a chamber. Electrical charges carried on aerosol charge carriers are used to charge small particles, which are then attracted to the outer walls, where they are carried away by the scavenging flow of the larger particles. The Kunsagi reference is designed for removal of particulates generated in combustion of coal, which are much larger than the particulates of the application contemplated herein. Thus, none of these references suggest a device or method for accomplishing the removal of particulates from a reactor gas stream in a suitable manner.
It is accordingly the primary objective of the present invention that it operate to remove substantially all of the particulates contained in the gas stream emanating from a reactor vessel. Thus, the particulate separator of the present invention must be operable on a continuous, high pressure gas stream including particulates to remove the particulates as efficiently as possible. The particulate separator must also be operable on the small particulates typically contained in a reactor vessel gas stream, which range from approximately two to five microns, and which have small settling rates.
It is a further objective of the present invention that it operate in a manner not requiring a scrubbing fluid, the use of which would further exacerbate the problem of substance disposal. In addition, the solution to the problems enumerated above should not involve the use of a filter medium, which may become clogged or which may require periodic maintenance or changing. It is an additional objective of the present invention that it operate to effectively separate the gas in the gas stream from particulates contained therein while using as little gas as possible.
It is a still further objective of the present invention that it be relatively compact and inexpensive, both to construct, as well as to operate and maintain. The particulate separator of the present invention should also enable the conversion of the high pressure gas stream containing particulates to a low pressure outlet flow of gas at a first output point, and a low pressure outflow of particulates and a small amount of gas at a second output point. Finally, it is also an objective that all of the aforesaid advantages and objectives be achieved without incurring any substantial relative disadvantage.